Intravascular stent

ABSTRACT

A stent in a non-expanded state has a first and second expansion column, each consisting of a plurality of expansion strut pairs. An expansion strut pair includes a first expansion strut, a second expansion strut and a joining strut that couples the first and second expansion struts at one end. Expansion strut pairs include expansion strut pair first and second corners formed where the joining strut couples the first and second expansion struts. A connecting strut column, formed of a plurality of connecting struts couples the first and second expansion columns. Connecting struts include a proximal section, a distal section and an intermediate section. The proximal section is coupled to the corner of an expansion strut pair of the first expansion column, and the distal section is coupled to the joining strut of an expansion strut pair of the second expansion column intermediate the expansion strut pair first corner and the expansion strut pair second corner.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/574,077, filed on May 18, 2000, now U.S. Pat. No. 6,770,088, which isa continuation of U.S. patent application Ser. No. 08/845,734, filed onApr. 25, 1997, now abandoned, which is a continuation-in-part of U.S.patent application Ser. No. 08/824,142, filed Mar. 25, 1997, now U.S.Pat. No. 6,241,760 and which is a continuation-in-part of U.S. patentapplication Ser. No. 08/824,866, filed Mar. 26, 1997, now U.S. Pat. No.5,954,743 and which is a continuation-in-part of U.S. patent applicationSer. No. 08/824,865, filed Mar. 26, 1997, now U.S. Pat. No. 6,152,957and which is a continuation-in-part of U.S. patent application Ser. No.08/845,657, filed Apr. 25, 1997, now U.S. Pat. No. 5,922,021, whichclaims the benefit of Provisional Patent Application No. 60/017,484filed Apr. 26, 1996, all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to intravascular stents, and more particularly toan intravascular stent which provides easy introduction through tortuoussections of vessels.

2. Description of the Related Art

Angioplasty, either coronary or general vascular, has advanced to becomethe most effective means for revascularization of stenosed vessels. Inthe early 1980's, angioplasty first became available for clinicalpractice in the coronary artery, and has since proven an effectivealterative to conventional bypass graft surgery. Balloon catheterdependent angioplasty has consistently proven to be the most reliableand practical interventional procedure. Other ancillary technologiessuch as laser based treatment, or directional or rotational arthrectomy,have proven to be either of limited effectiveness or dependent onballoon angioplasty for completion of the intended procedure. Restenosisfollowing balloon-based angioplasty is the most serious drawback and isespecially prevalent in the coronary artery system.

Many regimens have been designed to combat restenosis, with limitedsuccess, including laser based treatment and directional or rotationalarthrectomy. Intravascular stenting, however, noticeably reduces therestenosis rate following angioplasty procedures. The procedure forintravascular stent placement typically involves pre-dilation of thetarget vessel using balloon angioplasty, followed by deployment of thestent, and expansion of the stent such that the dilated vessel walls aresupported from the inside.

The intravascular stent functions as scaffolding for the lumen of avessel. The scaffolding of the vessel walls by the stent serve to: (a)prevent elastic recoil of the dilated vessel wall, (b) eliminateresidual stenosis of the vessel; a common occurrence in balloonangioplasty procedures, (c) maintain the diameter of the stented vesselsegment slightly larger than the native unobstructed vessel segmentsproximal and distal the stented segment and (d) as indicated by thelatest clinical data, lower the restenosis rate. Following anangioplasty procedure, the restenosis rate of stented vessels has provensignificantly lower than for unstented or otherwise treated vessels;treatments include drug therapy and other methods mentioned previously.

Another benefit of vessel stenting is the potential reduction ofemergency bypass surgery arising from angioplasty procedures. Stentinghas proven to be effective in some cases for treating impending closureof a vessel during angioplasty. Stenting can also control and stabilizean unstable local intimal tear of a vessel caused by normal conductduring an angioplasty procedure. In some cases, an incomplete or lessthan optimal dilatation of a vessel lesion with balloon angioplasty cansuccessfully be opened up with a stent implant.

Early in its development, the practice of stenting, especially incoronary arteries, had serious anticoagulation problems. However,anticoagulation techniques have since been developed and are becomingsimpler and more effective. Better and easier to use regimens arecontinuously being introduced, including simple outpatientanticoagulation treatments, resulting in reduced hospital stays forstent patients.

An example of a conventional stent patent is U.S. Pat. No. 5,102,417(hereafter the Palmaz Patent). The stent described in the Palmaz Patentconsists of a series of elongated tubular members having a plurality ofslots disposed substantially parallel to the longitudinal axis of thetubular members. The tubular members are connected by at least oneflexible connector member.

The unexpanded tubular members of the Palmaz Patent are overly rigid sothat practical application is limited to short lengths. Even withimplementation of the multilink design with flexible connector membersconnecting a series of tubular members, longer stents can not navigatetortuous blood vessels. Furthermore, the rigidity of the unexpandedstent increases the risk of damaging vessels during insertion.Foreshortening of the stent during insertion complicates accurateplacement of the stent and reduces the area that can be covered by theexpanded stent. There is, further, no method of programming the stentdiameter along its longitudinal axis to achieve a tapered expandedstent, and no method of reenforcement of stent ends or other regions isprovided for.

Another example of a conventional stent patent is WO 96/03092, the Brunpatent. The stent described in the Brun patent is formed of a tubehaving a patterned shape, which has first and second meander patterns.The even and odd first meander patterns are 180 degrees out of phase,with the odd patterns occurring between every two even patterns. Thesecond meander patterns run perpendicular to the first meander patterns,along the axis of the tube.

Adjacent first meander patterns are connected by second meander patternsto form a generally uniform distributed pattern. The symmetricalarrangement with first and second meander patterns having sharp rightangled bends allows for catching and snagging on the vessel wall duringdelivery. Furthermore, the large convolutions in the second meanderpattern are not fully straightened out during expansion reducingrigidity and structural strength of the expanded stent. There is,further, no method of programming the stent diameter along itslongitudinal axis to achieve a tapering stent design, and no method ofreenforcement of stent ends or other regions is provided for.

These and other conventional stent designs suffer in varying degreesfrom a variety of drawbacks including: (a) inability to negotiate bendsin vessels due to columnar rigidity of the unexpanded stent; (b) lack ofstructural strength, axio-lateral, of the unexpanded stent; (c)significant foreshortening of the stent during expansion; (d) limitedstent length; (e) constant expanded stent diameter; (f) poor crimpingcharacteristics; and (g) rough surface modulation of the unexpandedstent.

There is a need for a stent with sufficient longitudinal flexibility inthe unexpanded state to allow for navigation through tortuous vessels.There is a further need for a stent that is structurally strong in theunexpanded state such that risk of damage or distortion during deliveryis minimal. A further need exists for a stent that maintainssubstantially the same longitudinal length during expansion to allowgreater coverage at the target site and simplify proper placement of thestent. Yet a further need exists for a stent design with sufficientlongitudinal flexibility that long stents of up to 100 mm can be safelydelivered through tortuous vessels. There is a need for a stent that isconfigured to expand to variable diameters along its length, such that ataper can be achieved in the expanded stent to match the natural taperof the target vessel. A need exists for a stent which, (i) can becrimped tightly on the expansion balloon while maintaining a low profileand flexibility, (ii) has a smooth surface modulation when crimped overa delivery balloon, to prevent catching and snagging of the stent on thevessel wall during delivery or (iii) with reenforcement rings on theends or middle or both to keep the ends of the stent securely positionedagainst the vessel walls of the target blood vessel.

SUMMARY OF THE INVENTION

Accordingly an object of the present invention is to provide a scaffoldfor an interior lumen of a vessel.

Another object of the invention is to provide a stent which preventsrecoil of the vessel following angioplasty.

A further object of the invention is to provide a stent that maintains alarger vessel lumen compared to the results obtained only with balloonangioplasty.

Yet another object of the invention is to provide a stent that reducesforeshortening of a stent length when expanded.

Another object of the invention is to provide a stent with increasedflexibility when delivered to a selected site in a vessel.

A further object of the invention is to provide a stent with a lowprofile when crimped over a delivery balloon of a stent assembly.

Yet a further object of the invention is to provide a stent with reducedtuliping of a stent frame.

Another object of the invention is to provide a chain mesh stent thatreduces vessel “hang up” in a tortuous vessel or a vessel withcurvature.

A further object of the invention is to provide a chain mesh stent thatincreases radial and axio-lateral strength of the expanded stent.

These and other objects of the invention are achieved in a stent in anonexpanded state. A first expansion column includes of a plurality offirst expansion column strut pairs. A first expansion strut pairincludes a first expansion strut adjacent to a second expansion strutand a first joining strut that couples the first and second expansionstruts at a proximal end of the first expansion strut pair. A secondexpansion strut pair includes a third expansion strut adjacent to thesecond expansion strut and a second joining strut that couples thesecond and third expansion struts at a distal end of the secondexpansion strut pair. A third expansion strut pair includes a fourthexpansion strut adjacent to the third expansion strut and a thirdjoining strut that couples the third and fourth expansion struts at aproximal end of the third expansion strut pair. A fourth expansion strutpair includes a fifth expansion strut adjacent to the fourth expansionstrut and a fourth joining strut that couples the fourth and fifthexpansion struts at a distal end of the fourth expansion strut pair.

A first expansion strut pair first corner is formed where the firstjoining strut is coupled to the first expansion strut, and a firstexpansion strut pair second corner is formed where the first joiningstrut is coupled to the second expansion strut. A second expansion strutpair first corner is formed where the second joining strut is coupled tothe second expansion strut, and a second expansion strut pair secondcorner is formed where the second joining strut is coupled to the thirdexpansion strut. A third expansion strut pair first corner is formedwhere the third joining strut is coupled to the third expansion strut,and a third expansion strut pair second corner is formed where the thirdjoining strut is coupled to the fourth expansion strut. A fourthexpansion strut pair first corner is formed where the fourth joiningstrut is coupled to the fourth expansion strut, and a fourth expansionstrut pair second corner is formed where the fourth joining strut iscoupled to the fifth expansion strut.

A second expansion column includes of a plurality of second expansioncolumn strut pairs. A first expansion strut pair includes a firstexpansion strut adjacent to a second expansion strut and a first joiningstrut that couples the first and second expansion struts at a proximalend of the first expansion strut pair. A second expansion strut pairincludes a third expansion strut adjacent to the second expansion strutand a second joining strut that couples the second and third expansionstruts at a distal end of the second expansion strut pair. A thirdexpansion strut pair includes a fourth expansion strut adjacent to thethird expansion strut and a third joining strut that couples the thirdand fourth expansion struts at a proximal end of the third expansionstrut pair. A fourth expansion strut pair includes a fifth expansionstrut adjacent to the fourth expansion strut and a fourth joining strutthat couples the fourth and fifth expansion struts at a distal end ofthe fourth expansion strut pair.

A first expansion strut pair first corner is formed where the firstjoining strut is coupled to the first expansion strut, and a firstexpansion strut pair second corner is formed where the first joiningstrut is coupled to the second expansion strut. A second expansion strutpair first corner is formed where the second joining strut is coupled tothe second expansion strut, and a second expansion strut pair secondcorner is formed where the second joining strut is coupled to the thirdexpansion strut. A third expansion strut pair first corner is formedwhere the third joining strut is coupled to the third expansion strut,and a third expansion strut pair second corner is formed where the thirdjoining strut is coupled to the fourth expansion strut. A fourthexpansion strut pair first corner is formed where the fourth joiningstrut is coupled to the fourth expansion strut, and a fourth expansionstrut pair second corner is formed where the fourth joining strut iscoupled to the fifth expansion strut.

A first connecting strut column is formed of a plurality of firstconnecting struts, each connecting strut of the first connecting strutcolumn includes a connecting strut proximal section, a connecting strutdistal section and a connecting strut intermediate section. A firstconnecting strut proximal section is coupled to the first corner of thesecond expansion strut pair of the first expansion strut column, and afirst connecting strut distal section is coupled to the first joiningstrut of the first expansion strut pair of the second expansion strutcolumn intermediate the first expansion strut pair first corner and thefirst expansion strut pair second corner. A second connecting strutproximal section is coupled to the first corner of the fourth expansionstrut pair of the first expansion strut column, and a second connectingstrut distal section is coupled to the third joining strut of the thirdexpansion strut pair of the second expansion strut column intermediatethe third expansion strut pair first corner and the third expansionstrut pair second corner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side elevation view of the pre-expansion mode of anembodiment of the stent of the present invention;

FIG. 1B is a cross sectional view of an embodiment of the stent of thepresent invention;

FIG. 1C is a longitudinal cross sectional view of an embodiment of thestent of the present invention;

FIG. 2A is a scale drawing of the strut pattern of an embodiment of thestent of the present invention;

FIG. 2B is an expanded view of a section of the pattern of FIG. 2A;

FIG. 3A is a schematic illustration of a pre-expansion mode of anembodiment of the stent of the present invention;

FIG. 3B is a schematic illustration of the post-expansion mode of anembodiment of the stent of the present invention;

FIG. 4A is a scale drawing including dimensions of an embodiment of thestent of the present invention;

FIG. 4B is an enlarged section of the scale drawing of FIG. 4A;

FIG. 5A is a scale drawing of an embodiment of the stent of the presentinvention, the stent having a tapered diameter in its post-expansionmode;

FIG. 5B is a scale drawing an embodiment of the stent of the presentinvention, the stent having a tapered diameter in its post-expansionmode;

FIG. 5C is a schematic of an embodiment of the stent of the presentinvention in an expanded state with a tapered diameter;

FIG. 6A is a scale drawing of an embodiment of the stent of the presentinvention with reenforcement expansion columns;

FIG. 6B is a perspective view of the embodiment of FIG. 6A;

FIG. 6C is an expanded view of a section of the pattern of FIG. 6A.

FIG. 7A is a scale drawing of an embodiment of the stent of the presentinvention including relief notches at strut joints to increaseflexibility of the joints;

FIG. 7B is an enlarged region of the embodiment of FIG. 7A;

FIG. 7C is an enlarged view of a single connecting strut joining twoexpansion strut pairs in accordance with the embodiment of FIG. 7A;

FIG. 8A is a side elevation view of an embodiment of the stent of thepresent invention;

FIG. 8B is a side elevation view of an embodiment of the stent of thepresent invention, shown as if the stent struts and space there betweenwere transparent;

FIG. 8C is a scale drawing of an embodiment of the stent of the presentinvention;

FIG. 8D is a variation of the embodiment of the stent of FIG. 8C;

FIG. 8E is a perspective view of the embodiment of FIG. 8D;

FIG. 8F is a drawing illustrating the post-expansion mode of the stentof the embodiment of FIG. 8D of the present invention;

FIG. 8G is an enlarged view of a single connecting strut joining twoexpansion strut pairs in accordance with an embodiment of the presentinvention;

FIG. 9A is a side elevation view of an embodiment of the stent of thepresent invention;

FIG. 9B is a perspective view of the embodiment of FIG. 9A;

FIG. 9C is a scale drawing of the embodiment of FIG. 9A;

FIG. 9D is an enlarged region of the drawing of FIG. 9C;

FIG. 9E is a scale drawing of an embodiment of the stent of the presentinvention;

FIG. 9F is a scale drawing of an embodiment of the stent of the presentinvention;

FIG. 9G is an enlarged view of a single connecting strut joining twoexpansion strut pairs in accordance with an embodiment of the presentinvention;

FIG. 10A is a drawing of an alternate geometry of connecting struts andjoining struts in accord with the present invention;

FIG. 10B is a drawing of an alternate geometry of connecting struts andjoining struts in accord with the present invention;

FIG. 10C is a drawing of an alternate geometry of connecting struts andjoining struts in accord with the present invention;

FIG. 10D is a drawing of an alternate geometry of connecting struts andjoining struts in accord with the present invention;

FIG. 10E is a drawing of an alternate geometry of connecting struts andjoining struts in accord with the present invention;

FIG. 10F is a drawing of an alternate geometry of connecting struts andjoining struts in accord with the present invention; and

FIG. 11 is a delivery balloon catheter, illustrating a method of deliverof a stent in accord with the present invention.

DETAILED DESCRIPTION

A first embodiment of the present invention is shown in FIGS. 1A, 1B,1C, 2A and 2B. Referring to FIG. 1A, an elongate hollow tubular stent 10in an unexpanded state is shown. A proximal end 12 and a distal end 14define a longitudinal length 16 of stent 10. The longitudinal length 16of the stent 10 can be as long as 100 mm or longer. A proximal opening18 and a distal opening 20 connect to an inner lumen 22 of stent 10.Stent 10 can be a single piece, without any seams or welding joints ormay include multiple pieces.

Stent 10 is constructed of two to fifty or more expansion columns orrings 24 connected together by interspersed connecting strut columns 26.The first column on the proximal end 12 and the last column on thedistal end 14 of stent 10 are expansion columns 24.

Expansion columns 24 are formed from a series of expansion struts 28,and joining struts 30. Expansion struts 28 are thin elongate membersarranged so that they extend at least in part in the direction of thelongitudinal axis of stent 10. When an outward external force is appliedto stent 10 from the inside by an expansion balloon or other means,expansion struts 28 are reoriented such that they extend in a morecircumferential direction, i.e along the surface of cylindrical stent 10and perpendicular to its longitudinal axis. Reorientation of expansionstruts 28 causes stent 10 to have an expanded circumference anddiameter. In FIG. 1A, expansion struts 28 of unexpanded stent 10 areseen to extend substantially parallel to the longitudinal axis of stent10.

Expansion struts 28 are joined together by joining struts 30 to form aplurality of expansion strut pairs 32. Expansion strut pairs have aclosed end 34 and an open end 36. Additional joining struts 30 jointogether expansion struts 28 of adjacent expansion strut pairs 32, suchthat expansion struts 28 are joined alternately at their proximal anddistal ends to adjacent expansion struts 28 to form expansion columns24. Each expansion column 24 contains a plurality, typically eight totwenty, twenty to sixty, or larger of expansion struts 28. Expansioncolumns are preferably continuous unbroken ring structures extendingaround the circumference of the stent 10; however, broken structures inwhich individual struts or pieces of struts are removed from anotherwise continuous expansion column 24 can also be used.

Connecting struts 38 connect adjacent expansion columns 24 forming aseries of interspersed connecting strut columns 26 each extending aroundthe circumference of stent 10. Each connecting strut 38 joins a pair ofexpansion struts 28 in an expansion column 24 to an adjacent pair ofexpansion struts 28 in an adjacent expansion column 24. For stent 10 ofFIG. 1A, the ratio of expansion struts 28 in an expansion column 24 toconnecting struts 38 in a connecting strut column 26 is two to one;however, this ratio in general can be x to 1 where x is greater or lessthan two. Furthermore, since the stent 10 of FIG. 1A begins with anexpansion column 24 on the proximal end 12 and ends with an expansioncolumn 24 on the distal end 14, if there are n expansion columns 24 withm expansion struts 28 per column, there will be m−1 connecting strutcolumns 26, and n(m−1)/2 connecting struts 38.

The reduced number of connecting struts 38 in each connecting strutcolumn 26, as compared to expansion struts 28 in each expansion column24, allows stent 10 to be longitudinally flexibility. Longitudinalflexibility can be further increased by using a narrow width connectingstrut, providing additional flexibility and suppleness to the stent asit is navigated around turns in a natural blood vessel.

At least a portion of the open spaces between struts in stent 10 formasymmetrical cell spaces 40. A cell space or geometric cell is an emptyregion on the surface of stent 10, completely surrounded by one or acombination of stent struts, including expansion struts 28, connectingstruts 38, or joining struts 30. Asymmetrical cell spaces 40 are cellspaces which have no geometrical symmetry i.e. no rotation, reflection,combination rotation and reflection or other symmetry. Asymmetrical cellspaces 40 have an asymmetrical geometric configuration.

Asymmetrical cell spaces 40 in FIG. 1A are surrounded by a firstexpansion strut pair 32 in a first expansion column 24, a firstconnecting strut 38, a second expansion strut pair 32 in an adjacentexpansion column 24, a first joining strut 30, a second connecting strut38, and a second joining strut 30. Furthermore, expansion strut pairs 32of asymmetrical cell space 40 may be circumferentially offset i.e. havelongitudinal axes that are not collinear and have their open ends 36facing each other. The space between two expansion struts of anexpansion strut pair 32 is known as a loop slot 42.

FIG. 1B shows inner lumen 22, radius 44 and stent wall 46 of stent 10.Stent wall 46 consists of stent struts including expansion struts 28,connecting struts 38 and joining struts 30.

FIG. 1C shows, proximal end 12, distal end 14, longitudinal length 16,inner lumen 22, and stent wall 46 of stent 10. Inner lumen 22 issurrounded by stent wall 46 which forms the cylindrical surface of stent10.

Referring now to FIGS. 2A and 2B, joining struts 30 of stent 10 are seento extend at an angle to the expansion struts 28, forming a narrow angle48 with one expansion strut 28 in an expansion strut pair 32 and a wideangle 50 with the other expansion strut 28 of an expansion strut pair32. Narrow angle 48 is less than ninety degrees, while wide angle 50 isgreater than ninety degrees. Joining struts 30 extend bothlongitudinally along the longitudinal axis of stent 10 andcircumferentially, along the surface of the stent 10 perpendicular toits longitudinal axis.

Expansion strut spacing 52 between adjacent expansion struts 28 in agiven expansion column 24 are uniform in stent 10 of FIGS. 2A and 2B;however, non-uniform spacings can also be used. Expansion strut spacings52 can be varied, for example, spacings 52 between adjacent expansionstruts 28 in an expansion column 24 can alternate between a narrow and awide spacings. Additionally, spacings 52 in a single expansion column 24can differ from other spacings 52 in other columns 24.

It is noted that varying expansion strut spacings 52 which form the loopslots 42 results in variable loop slot widths. Furthermore, thelongitudinal axis of the loop slots 42 need not be collinear or evenparallel with the longitudinal axis of loop slots 42 of an adjacentexpansion column 24. FIGS. 2A and 2B show an arrangement of expansionstruts 28 such that collinear, parallel adjacent loop slots 42 areformed, but non-collinear and non-parallel loop slots 42 can also beused.

Additionally the shape of loop slots 42 need not be the same among loopslots of a single or multiple expansion columns 24. The shape of loopslots 42 can be altered by changing the orientation or physicaldimensions of the expansion struts 28 and/or joining struts 30 whichconnect expansion struts 28 of expansion strut pairs 32 defining theboundaries of loop slots 42.

Connecting struts 38 couple adjacent expansion columns 24, by connectingthe distal end of an expansion strut pair in one expansion column 24 tothe proximal end of an adjacent expansion strut pair 32 in a secondexpansion column 24. Connecting struts 38 of FIGS. 2A and 2B are formedfrom two linear sections, a first linear section 54 being joined at itsdistal end to a second linear section 56 at its proximal end to form afirst slant angle 58.

The first linear section 54 of a connecting strut 38 is joined toexpansion strut 28 at the point where joining strut 30 makes narrowangle 48 with expansion strut 28. First linear section 54 extendssubstantially collinear to joining strut 30 continuing the line ofjoining strut 30 into the space between expansion columns 24. The distalend of the first linear section 54 is joined to the proximal end of thesecond linear section 56 forming slant angle 58. Second linear section56 extends substantially parallel to expansion struts 28 connecting atits distal end to joining strut 30 in an adjacent expansion column 24.The distal end of second linear section 56 attaches to expansion strut28 at the point where joining strut 30 makes narrow angle 48 withexpansion strut 28. Further, joining strut 30 can have a second slantangle with a width that can be the same or different from the width ofthe first slant angle.

FIGS. 2A and 2B show connecting struts 38 and joining struts 30 slantedrelative to the longitudinal axis of stent 10, with the circumferentialdirection of the slanted struts alternating from column to adjacentcolumn. Circumferential direction refers to the handedness with whichthe slanted struts wind about the surface of the stent 10. Thecircumferential direction of the slant of connecting strut first linearsections 54 in a connecting strut column 26 is opposite thecircumferential direction of the slant of connecting strut first linearsections 54 in an adjacent connecting strut column 26. Similarly, thecircumferential direction of the slant of joining struts 30 in anexpansion column 24 is opposite the circumferential direction of theslant of joining struts 30 in an adjacent expansion column 24.Alternating circumferential slant directions of connecting struts 38 andjoining struts 30 prevents axial warping of stent 10 during deliver andexpansion. Other non-alternating slant direction patterns can also beused for connecting struts 38 or joining struts 30 or both.

FIGS. 3A and 3B show a schematic illustration of a stent designaccording to the present invention in an unexpanded and expanded staterespectively. The design is depicted as a flat projection, as if stent10 were cut lengthwise parallel to its longitudinal axis and flattenedout. The connecting struts 38 consist of first and second linearsections 54 and 56 forming slant angle 58 at pivot point 60. Anasymmetrical cell space 40 is formed by expansion strut pairs 32,connecting struts 38 and joining struts 30. Multiple interlockingasymmetrical cell spaces 40 make up the design pattern.

As the stent is expanded, see FIG. 3B, the expansion strut pairs 32spread apart at their open ends 36, shortening the length of expansionstruts 28 along the longitudinal axis of the cylindrical stent. Thelongitudinal shortening of expansion struts 28 during expansion iscountered by the longitudinal lengthening of connecting struts 38. Thewidening of slant angle 58 during expansion straightens connectingstruts 38 and lengthens the distance between the coupled expansion strutpairs 32. The widening of the slant angle of connecting struts 38substantially compensates for the longitudinal shortening of expansionstruts 28. Thus, the stent has substantially constant unexpanded andexpanded longitudinal lengths.

When the stent is expanded, each expansion column 24 becomescircumferentially stretched, enlarging the space between struts. Theinterlinking of expansion columns 24 by connecting struts 38 that havebeen straightened through the expansion process gives the stent 10 ahigh radial support strength. The entire stent 10 when expanded isunitized into a continuous chain mesh of stretched expansion columns 24and connecting strut columns 26 forming an asymmetrical interlockingcell geometry which resists collapse both axially and radially. When thestent is expanded it has increased rigidity and fatigue tolerance.

In addition, efficient bending and straightening of connecting struts 38at pivot points 60 allows increased longitudinal flexibility of thestent. For the stent to bend longitudinally, at least some of connectingstruts 38 are forced to bend in their tangent plane. The tangent planeof a specific connecting strut 38 refers to the plane substantiallytangent to the cylindrical surface of the stent at that connecting strut38. The width of connecting struts 38 can be twice as wide as athickness. Preferably, a one-to-one ratio is preferred. However, pivotpoints 60 in connecting struts 38 provide connecting struts 38 aflexible joint about which to more easily bend increasing longitudinalflexibility of the stent.

Referring to FIGS. 4A and 4B, a variation of the first embodiment ofstent 10 of the present invention is shown. In this variation, stent 10has a length 16 of 33.25 mm and an uncrimped and unexpandedcircumference 88 of 5.26 mm. Fifteen expansion columns 24 areinterspersed with connecting strut columns 26. Each expansion column 24consists of twelve expansion struts 28 joined alternately at theirproximal and distal ends by joining struts 30 forming six expansionstrut pairs 32. Expansion struts 28 are aligned parallel to thelongitudinal axis of cylindrical stent 10. Joining struts 30 form anarrow angle 48 and a wide angle 50 with the respective expansion struts28 of expansion strut pairs 32. Adjacent expansion columns 24 employalternating circumferential slant directions of joining struts 30.

In this variation of the first embodiment, expansion strut width 62 is0.20 mm, expansion strut length 64 is 1.51 mm, and connecting strutwidth 66 is 0.13 mm. Distance 68 from the outer edge of a firstexpansion strut 28 to the outer edge of a second adjacent expansionstrut 28 in the same expansion column 24 is 0.64 mm, leaving a loop slotwidth 70 of 0.24 mm.

In this variation of the first embodiment, connecting struts 38 consistof a slanted first linear section 54 joined to a second linear section56 at a slant angle 58. First linear section 54 is slightly longer thansecond linear section 56 and is attached at its proximal end to anexpansion strut 28 in an expansion column 24. The attachment of theproximal end of first linear section 54 to expansion strut 28 is at thepoint where joining strut 30 makes narrow angle 48 with expansion strut28. First linear section 54 extends substantially collinear to joiningstrut 30 attaching at its distal end to the proximal end of secondlinear section 56 to form slant angle 58. Second linear section 56extends substantially collinear to expansion struts 28, attaching at itsdistal end to an expansion strut 28 in an adjacent expansion column 24.The attachment occurs at the point where expansion strut 28 forms narrowangle 48 with joining strut 30. Joining struts 30 and connecting strutfirst linear sections 54 slant in alternating circumferential directionsfrom column to adjacent column.

The joining of connecting struts 38 and expansion struts 28 at the pointwhere narrow angle 48 is formed aids smooth delivery of stent 10 bystreamlining the surface of the unexpanded stent and minimizing possiblecatching points. Bare delivery of stent 10 to the target lesion in avessel will thus result in minimal snagging or catching as it isnavigated through turns and curvatures in the vessel. Stent 10 behaveslike a flexible, tubular sled as it is moved forward or backward in thevessel on the delivery catheter, sliding through tortuous vessels andover irregular bumps caused by atherosclerotic plaques inside the vessellumen.

When fully expanded Stent 10 of FIGS. 4A and 4B has an internal diameterof up to 5.0 mm, while maintaining an acceptable radial strength andfatigue tolerance. The crimped stent outer diameter can be as small as1.0 mm or less depending on the condition of the underlying deliveryballoon profile; A small crimped outer diameter is especially importantif stent delivery is to be attempted without predilation of the targetsite. When the stent is optimally crimped over the delivery balloon, thesurface of the crimped stent is smooth allowing for no snagging of thestent struts during either forward or backward movement through avessel.

FIGS. 5A and 5C shows a second embodiment of the present invention inwhich the stent 10 in its expanded form has a gradual taper fromproximal end 12 to distal end 14. In FIG. 5A, the shaded segments 72,74, 76, 78, 80, 82 and 84 of expansion struts 28 represent regions ofexpansion struts 28 to be removed. As shown schematically in FIG. 5C,removal of the shaded segments 72, 74, 76, 78, 80, 82, and 84 providesstent 10 with a gradual taper when expanded with distal end 14 having asmaller expanded diameter than proximal end 12, The degree of shorteningof the expanded diameter of the stem 10 at a given expansion column 24will be proportional to the length of the removed segment 72, 74, 76,78, 80, 82, or 84 at that expansion column 24. In the expanded stent 10the shortened expansion struts 28 will have a shortened component alongthe circumference of the stent resulting in a shortened circumferenceand diameter. The tapered diameter portion can be positioned anywherealong the length of stent 10, and the tapering can be made more or lessgradual by removing appropriately larger or smaller portions of theexpansion struts 28 in a given expansion column 24.

Tapering is especially important in long stents, longer than 12 mm,since tapering of blood vessels is more pronounced over longer lengths.A long stent with a uniform stent diameter can only be matched to thetarget vessel diameter over a short region. If the proximal vessel sizeis matched with the stent diameter, the expanded distal end of the stentwill be too large for the natural vessel and may cause an intimaldissection of the distal vessel by stent expansion. On the other hand,if the distal vessel size is matched with the stent diameter, theproximal end of the expanded stent will be too small to set inside thevessel lumen. It is therefore desirable to have a stent with a taperedexpanded diameter.

Another way to achieve a tapered expanded stent is to change thestiffness of the stent struts, expansion struts, connecting struts orjoining struts such that the stiffness of the struts varies along thelength of the stent. The stiffness of the struts can be changed byaltering length, width or thickness, adding additional stiffeningmaterial, using a chemical or mechanical means to alter the physicalproperties of the stent material, or applying one or a series of elasticelements about the stent. FIG. 5B shows an embodiment of the presentinvention where the stiffness of the connecting struts is change byaltering the length of the connecting struts as described above. Theshaded segments 72, 74, 76, 78, 80, 82 and 84 of connection struts 38represent regions of connection struts 38 to be removed in order toprovide the tapered configuration described. A stent having thisconfiguration is shown in FIG. 5C in the expanded state.

Along with the use of a tapered diameter stent, a matching taperedballoon catheter would ideally be made for delivery and deployment ofthe tapered diameter stent. The method of using a tapered matchingballoon catheter with a tapered diameter stent is within the scope ofthe present invention.

Using a tapered balloon to expand a non-tapered stent will also achievea tapered expanded stent; however, since no metal is removed from thestent, the stent is tapered as a result of incomplete expansion. Thestent will therefore have increased metal fraction at the tapered endresulting in increased risk of acute thrombosis. Metal fraction is thepropostion of the surface of the expanded stent covered by the stentstrut material. Shortening the expansion struts as shown in FIGS. 5A and5C allows for a tapered expanded stent with substantially constant metalfraction along its length.

A third embodiment of the present invention shown in FIGS. 6A, 6B and 6Chas multiple reinforcement expansion columns 86 placed along the lengthof the stent 10. The reinforcement columns 86 are placed along the stentlength to provide additional localized radial strength and rigidity tostent 10. Additional strength and rigidity are especially important atthe ends of the stent to prevent deformation of the stent both duringdelivery and after placement. During delivery the stent ends can catchon the vessel wall possibly deforming the unexpanded stent and alteringits expansion characteristics. After the stent has been placed it isimportant that the stent ends are rigid so that they set firmly againstthe vessel wall, otherwise, during a subsequent catheter procedure, thecatheter or guidewire can catch on the stent ends pulling the stent awayfrom the vessel wall and possibly damaging and/or blocking the vessel

The specific variation of the third embodiment of stent 10 depictedFIGS. 6A, 6B and 6C has a length 16 of 20.70 mm and an uncrimped andunexpanded circumference 88 of 5.26 mm. The stent 10 consists of sixexpansion columns 24 and three reinforcement expansion columns 86, eachconsisting respectively of twelve expansion struts 28 or reenforcementexpansion struts 90. The reenforcement expansion columns 86 arepositioned one at either end, and one along the length of the stent 10.

The expansion strut width 62 is 0.15 mm, reenforcement expansion strutwidth 92 is 0.20 mm, and the connecting strut width 66 is 0.10 mm. Thenarrow angle 48 formed by joining strut 30 and expansion strut 28 is 75degrees, and the narrow angle 94 formed by reenforcement joining strut96 and reenforcement expansion strut 90 is 60 degrees.

Other arrangements of reenforcement expansion columns 86, such asproviding reenforcement expansion columns 86 only on the ends of thestent, only on one end, or at multiple locations throughout the lengthof the stent can also be used and fall within the scope of the presentinvention. A taper can also be programmed into the reenforced stent 10by shortening expansion struts 28 and reenforcement expansion struts 90in appropriate expansion columns 24 and 86.

A fourth embodiment of the present invention, shown in the FIGS. 7A, 7Band 7C, is similar to the third embodiment but has the added feature ofrelief notches 98 and 100. A relief notch is a notch where metal hasbeen removed from a strut, usually at a joint where multiple struts areconnected. Relief notches increase flexibility of a strut or joint bycreating a thinned, narrow region along the strut or joint. Relief notch98 is formed at the joint formed between first linear section 54 ofconnecting strut 38 and expansion strut 28. Relief notch 100 is formedat the joint between second linear section 56 of connecting strut 38 andexpansion strut 28. The positioning of the relief notches gives addedflexibility to the unexpanded stent and prevents warping at the jointswhen the stent is expanded. This results in a smooth surface modulationto the expanded stent frame. Relief notches can be placed at otherjoints and can be included in any of the previously mentionedembodiments.

FIGS. 8A and 8B show a side elevation view of a variation of the fifthembodiment of the stent of the present invention. In this embodiment afour piece slanted connecting strut 38 is used to couple the corner ofan expansion strut pair 32 in one expansion column 24 to the joiningstrut 30 of a circumferentially offset expansion strut pair 32 in anadjacent expansion column 24. The expansion struts 28, joining struts30, expansion columns 24, reenforcement expansion struts 90,reenforcement joining struts 96, and reenforcement expansion columns 86are substantially similar to the fourth embodiment of FIG. 6A.Connecting struts 38 in connecting strut columns 26, however, have analtered geometry and connectivity; described in more detail below.

FIG. 8A shows only the stent struts on the front half of the stentsurface. The stent struts on the rear half of the stent surface are notshown. The stent appears as it would if the stent struts and space therebetween were opaque. FIG. 8B shows all stent struts from both the frontand rear halves. The stent appears as it would if the stent struts andthe space there between were transparent.

A first variation of a fifth embodiment of the present invention, shownin FIG. 8C consists of a stent 10 with twelve expansion columns 24, fourreenforcement expansion columns 86, and fifteen connecting strut columns26. In this variation, the stent 10 has a length 16 of 31.96 mm, and anunexpanded circumference 88 of 5.26 mm.

Connecting struts 38 shown in an enlarged view in FIG. 8G are made up offour linear sections, a proximal end section 162, first and secondintermediate sections 164 and 166 respectively and a distal end section168 forming three slant angles 170, 172 and 174. The proximal end ofproximal section 162 is attached to a corner 176 of an expansion strutpair 32 of an expansion column 24. Corner 176 is formed where joiningstrut 30 makes narrow angle 48 with expansion strut 28. A second corner178 of expansion strut 32 is formed where joining strut 30 makes wideangle 50 with expansion strut 28. Corners 176 and 178 can have anangular shape formed by joining linear expansion struts 28 and joiningstruts 30, or preferably corners 176 and 178 are rounded to remove sharpedges and provide increased flexibility. Additionally rounded cornersprovide stent 10 with greater expandability and reduce stress in thestent strut material at the corners in the expanded stent.

Proximal end section 162 of connecting strut 38 extends from corner 176and is attached at its distal end to first intermediate section 164forming slant angle 170. First intermediate section 164 extends fromproximal end section 162 such that first intermediate section 164 isparallel to expansion struts 28 and is connected at its distal end tothe proximal end of second intermediate section 166 forming slant angle172.

Second intermediate section 166 extends in a slanted orientationrelative to the longitudinal axis of stent 10, extending bothlongitudinally along and circumferentially about stent 10. Preferably,second intermediate section 166 is parallel to joining strut 30 of thecircumferentially offset expansion strut pair 32 in adjacent expansioncolumn 24.

Second intermediate section 166 attaches at its distal end to theproximal end of distal end section 168 forming slant angle 174. Distalend section 168 extends from second intermediate section 166 attachingat its distal end to joining strut 30 of circumferentially offsetexpansion strut pair 32 of adjacent expansion column 24. The attachmentis at a point intermediate corners 176 and 178, where joining strut 30forms narrow angle 48 and wide angle 50 respectively with expansionstruts 28.

The connection point of distal end section 168 to joining strut 30 iscloser to corner 176 than corner 178. Preferably the connection point isone to two or more expansion strut widths from corner 176. Offsettingthe connection point of distal end section 168 to joining strut 30 fromcorner 176 to a point intermediate corner 176 and corner 178 reduceswarping of the expanded stent 10, resulting in a smooth surfacemodulation and reduced risk of thrombosis. Additionally, this designprovides a longer total straightened length of connecting strut 38,which further reduces foreshortening of stent 10 during expansion.

A second variation of a fifth embodiment of the present invention, shownin an unexpanded form in FIGS. 8D, 8E and in an expanded form in FIG. 8Fconsists of a stent 10 with six expansion columns 24, two reenforcementexpansion columns 86, and seven connecting strut columns 26. In thisvariation, the stent 10 has a length 16 of 15.04 mm, and an unexpandedcircumference 88 of 5.26 mm. The stent design 10 is substantiallysimilar to the design of the first variation of the fifth embodiment ofFIG. 8C with a reduced number of expansion columns, reenforcementexpansion columns, and connecting strut columns.

FIG. 8F illustrates a portion of the expanded stent 10 of the secondvariation of the fifth embodiment. After expansion of stent 10 byballoon or other means, the expansion struts 28 are spread apartcircumferentially, increasing the separation at the open end 36 ofexpansion strut pairs 32 resulting in an increase in the circumferenceof the stent 10. The spreading of the expansion struts 28 causes alongitudinal shortening of the expansion columns 24, which iscompensated by a straightening of the connecting struts 38. During theexpansion process, the slant angles 170, 172 and 174 widen straighteningthe connection struts 38, and causing an increase in the separationdistance between adjacent expansion columns 24. The asymmetricalinterlocking cell geometry of the expanded stent is illustrated in FIG.8F.

FIGS. 9A, 9B, 9C, 9D, 9E, 9F and 9G illustrate a sixth embodiment of thestent of the present invention. In this embodiment a three piece slantedconnecting strut 38 is used to couple the joining strut 30 of anexpansion strut pair 32 in one expansion column 24 to the joining strut30 of a circumferentially offset expansion strut pair 32 in an adjacentexpansion column 24. The joints between segments of connecting strut 38are curved forming a smooth rounded shape. The expansion struts 28,joining struts 30, expansion columns 24, reenforcement expansion struts90, reenforcement joining struts 96, and reenforcement expansion columns86 are substantially similar to the fourth embodiment of FIG. 8A.Connecting struts 38 in connecting strut columns 26, however, have analtered geometry and connectivity, described in more detail below.

A first variation of a sixth embodiment of the present invention, shownin FIGS. 9A, 9B and 9C consists of a stent 10 with eight expansioncolumns 24, three reenforcement expansion columns 86, and ten connectingstrut columns 26. In this variation, the stent 10 has a length 16 of20.32 mm.

Relief notches 204 are utilized at the joints between reenforcementexpansion struts 90 and reenforcement joining struts 96 in thereenforcement expansion columns 86 at the stent proximal end 12 anddistal end 14. Relief notches 204 reduce the width of the joints betweenreenforcement expansion struts 90 and reenforcement joining struts 96,which reduces stress in the metal at the joints during and afterexpansion of the stent. Relief notches 204 are particularly important atthe stent ends since the stent ends are especially susceptible towarping during and after expansion. Preferably relief notches 204 reducethe joint widths, such that the joint widths are substantially the sameas the thickness of stent wall 46 (see FIGS. 1B and 1C).

Connecting struts 38 shown in an enlarged view in FIG. 9D are made up ofthree linear sections, a proximal end section 194, an intermediatesection 196 and a distal end section 198 forming two slant angles 200,202. The connecting struts 38 have wide radii of curvature at the jointsbetween connecting strut sections 194, 196 and 198. The shape ofconnecting strut 38 is thus curved or wavy rather than jagged andangular. The slant angles 200 and 202 are defined by linearlyextrapolating proximal end section 194, intermediate section 196 anddistal end section 198, as shown by the dotted lines in FIG. 9D.

FIG. 9E shows a variation of the connecting strut design of the sixthembodiment of the present invention. The connecting strut 38 of FIG. 9Ehas smaller radii of curvature at the joints between proximal endsection 194, intermediate section 196 and distal end section 198.Connecting strut 38 of FIG. 9E is thus more jagged and angular than thatof FIG. 9D.

Referring to the connecting struts 38 of FIG. 9D and 9E, the proximalend of proximal section 194 is attached to joining strut 30 of expansionstrut pair 32 intermediate corners 176 and 178. Proximal end section 194of connecting strut 38 extends from joining strut 30 and is attached atits distal end to intermediate section 196 forming slant angle 200.Intermediate section 196 extends from proximal end section 194 in aslanted orientation relative to the longitudinal axis of stent 10,extending both longitudinally along and circumferentially about stent10. Intermediate section 196 is preferably parallel to joining struts 30of coupled expansion strut pairs 32.

Intermediate section 196 is connected at its distal end to the proximalend of distal end section 198 forming slant angle 202. Distal endsection 198 extends from second intermediate section 196 attaching atits distal end to joining strut 30 of circumferentially offset expansionstrut pair 32 of adjacent expansion column 24. The attachment is at apoint intermediate corners 176 and 178, where joining strut 30 formsnarrow angle 48 and wide angle 50 respectively with expansion struts 28.

The connection point of proximal end section 194 and distal end section198 to joining struts 30 is closer to corner 176 than corner 178.Preferably the connection point is one to two or more expansion strutwidths from corner 176. Offsetting the connection point of distal endsection 198 to joining strut 30 from corner 176 to a point intermediatecorner 176 and corner 178 reduces warping of the expanded stent 10,resulting in a smooth surface modulation and reduced risk of thrombosis.Additionally, this design provides a longer total straightened length ofconnecting strut 38, which further reduces foreshortening of stent 10during expansion.

The connecting strut 38 of the sixth embodiment has one hundred andeighty degree rotational symmetry about its center. The symmetry of theconnecting strut 38 does not, however, result in a symmetrical cellspace as the width of loop slots 42 connected in each cell space aredifferent. Adjacent loop slots 42 in each expansion column havealternating narrow and wide widths, preserving the asymmetry of the cellspaces. Introduction of one or many symmetrical cell spaces can beachieved in this design e.g. by providing uniform loop slot width toloop slots in adjacent expansion columns 24 contained in the same cellspace. Additionally completely non-uniform cell space patterns utilizingsymmetric or asymmetric cell spaces can be achieved e.g. by providingnon-uniform variations in the widths of loop slots 42.

A second variation of a sixth embodiment of the present invention .shown in an unexpanded form in FIG. 9F consists of a stent 10 with six10 expansion columns 24, three reenforcement expansion columns 86, andeight connecting strut columns 26. In this variation, the stent 10 has alength 16 of 16.00 mm, and an unexpanded circumference 88 of 5.26 mm.The stent design 10 is substantially similar to the design of the firstvariation of the sixth embodiment of FIGS. 9A, 9B and 9C with a reducednumber of expansion columns 24 and connecting strut columns 26.

A third variation of a sixth embodiment of the present invention, shownin an unexpanded form in FIG. 9F consists of a stent 10 with twelveexpansion columns 24, four reenforcement expansion columns 86, andfifteen connecting strut columns 26. In this variation, the stent 10 hasa length 16 of 30.01 mm, and an unexpanded circumference 88 of 5.26 mm.The stent design 10 is substantially similar to the design of the firstvariation of the sixth embodiment of FIGS. 9A, 9B and 9C with anincreased number of expansion columns 24 reenforcement expansion columns86 and connecting strut columns 26.

FIGS. 10A, 10B, 10C, 10D, 10E and 10F illustrate some examples ofalternate connecting strut designs which can be used in any of thepreviously discussed embodiments. FIG. 10A shows a rounded loopconnecting strut 38 which joins two circumferentially offset expansionstrut pairs 32 in adjacent expansion columns. Expansion struts 28 ineach expansion strut pair 32 are joined by a joining strut 30. Joiningstruts 30 are slanted such as to form a narrow angle 48 and a wide angle50 with the expansion struts 28 they connect. The rounded loopconnecting strut 38 connects expansion struts 28 at the point wherenarrow angle 48 is formed between expansion struts 28 and joining struts30. The slopes of the rounded connecting strut 38 at its proximal end102 and distal end 104 substantially match the slopes of the joiningstruts 30 connecting the pairs of expansion struts 28. The rounded loopconnecting strut 38 thus blends smoothly into the joining struts 30.Additionally the rounded loop connecting strut 38 has a first radius ofcurvature 106 and a second radius of curvature 108.

In the design of FIG. 10B a rounded loop connecting strut 38 joins twocircumferentially offset expansion strut pairs 32 in adjacent expansioncolumns. Expansion struts 28 in each expansion strut pair 32 are joinedby a joining strut 30. Joining struts 30 are at right angles to theexpansion struts 28 they connect. The rounded loop connecting strut 38connects to expansion struts 28 at the same point as joining struts 30.The rounded connecting strut 38 has a first radius of curvature 106 anda second radius of curvature 108 such that it connects circumferentiallyoffset expansion strut pairs 32.

In the design of FIG. 10C connecting strut 38 joins twocircumferentially offset expansion strut pairs 32 in adjacent expansioncolumns. Expansion struts 28 in each expansion strut pair 32 are joinedby a joining strut 30. Joining struts 30 are slanted such as to form anarrow angle 48 and a wide angle 50 with the expansion struts 28 theyconnect. The connecting strut 38 connects expansion struts 28 at thepoint where narrow angle 48 is formed between expansion strut 28 andjoining strut 30.

The connecting strut 38 is made up of three linear sections 110, 112,and 114 forming two slant angles 116 and 118. The proximal end ofsection 110 is attached to expansion strut 28 at the point where joiningstrut 30 forms narrow angle 48 with expansion strut 28. Section 110extends substantially collinear to joining strut 30 and is attached atits distal end to intermediate section 112 forming slant angle 116.Intermediate section 112 extends at an angle to section 110 such thatintermediate section 112 is substantially parallel to expansion struts28 and is connected at its distal end to the proximal end of distalsection 114 forming slant angle 118. Distal section 114 extends at anangle such that it is substantially collinear to joining strut 30 of theadjacent expansion strut pair 32. Distal section 114 attaches at itsdistal end to expansion strut 28 of the adjacent expansion strut pair32, at the point where joining strut 30 forms narrow angle 48 withexpansion strut 28.

In the design of FIGS. 10D and 10E a connecting strut 38 joins twocircumferentially offset expansion strut pairs 32 in adjacent expansioncolumns. Expansion struts 28 in each expansion strut pair 32 are joinedby a joining strut 30. Joining struts 30 are at right angles to theexpansion struts 28 they connect. The connecting strut 38 connects toexpansion struts 28 at the same point as joining struts 30.

The connecting struts 38 of FIGS. 10D and 10E are made up of multipleconnecting strut sections connected end to end to form a jaggedconnecting strut 38 with multiple slant angles, coupling expansion strutpair 32 to adjacent expansion strut pair 32. The connecting strut ofFIG. 10D is made up of three connecting strut sections, a proximalsection 120, an intermediate section 122 and a distal section 124defining two slant angles 126 and 128, while the connecting strut ofFIG. 10E consists of four connecting strut sections, a proximal section130, intermediate sections 132 and 134, and a distal section 136defining three slant angles 138, 140 and 142. In addition, connectingstrut section 134 can be modified by replacing connecting strut section136 by the dotted connecting strut section 144 to give another possiblegeometry of connecting struts 38.

In the design of FIG. 10F connecting strut 38 joins twocircumferentially offset expansion strut pairs 32 in adjacent expansioncolumns. Expansion struts 28 in each expansion strut pair 32 are joinedby a joining strut 30. Joining struts 30 are slanted such as to form anarrow angle 48 and a wide angle 50 with the expansion struts 28 theyconnect.

Connecting strut 38 is made up of four linear sections, a proximal endsection 180, first and second intermediate sections 182 and 184respectively and a distal end section 186 forming three slant angles188, 190 and 192. The proximal end of section 180 is attached to corner176 at the point where joining strut 30 forms narrow angle 48 withexpansion strut 28. Proximal end section 180 extends at an angle tojoining strut 30 and is attached at its distal end to first intermediatesection 182 forming slant angle 188. First intermediate section 182extends at an angle to proximal end section 180 such that firstintermediate section 182 is substantially parallel to expansion struts28 and is connected at its distal end to the proximal end of secondintermediate section 184 forming slant angle 190. Second intermediatesection 184 is substantially longer than the first intermediate section182. Second intermediate section 184 extends at an angle such that it issubstantially collinear to joining strut 30 of the adjacent expansionstrut pair 32. Second intermediate section 184 attaches at its distalend to the proximal end of distal end section 186 forming slant angle192. Distal end section 186 extends in a slightly sloping orientationrelative to expansion struts 28, attaching to corner 176 of expansionstrut pair 32 where joining strut 30 forms narrow angle 48 withexpansion strut 28. Relief notches 206 are formed at the joint betweendistal end segment 186 of connecting strut 38 and corner 176 ofexpansion strut pair 32 to increase flexibility of the unexpanded stentand prevent warping when the stent is expanded.

One skilled in the art will recognize that there are many possiblearrangements of connecting struts and joining struts consistent with thepresent invention; the above examples are not intended to be anexhaustive list. In particular, it is noted that (a) connecting strutsections need not be linear but may contain one or many radii ofcurvature, (b) connecting strut sections may each have a differentlongitudinal axis, (c) the joint between connecting strut sections neednot be jagged or sharp, but rather can be smooth containing one ormultiple radii of curvature, and (d) relief notches may be present atany of the strut joints.

The stent of the present invention is ideally suited for application incoronary vessels although versatility in the stent design allows forapplications in non-coronary vessels, the aorta, and nonvascular tubularbody organs.

Typical coronary vascular stents have expanded diameters that range from2.5 to 5.0 mm. However, a stent with high radial strength and fatiguetolerance that expands to a 5.0 mm diameter may have unacceptably highstent metal fraction when used in smaller diameter vessels. If the stentmetal fraction is high, the chances of acute thrombosis and restenosispotential will increase. Even with the same metal fraction a smallercaliber vessel is more likely than a larger one to have a high rate ofthrombosis. It is, therefore, preferred to have at least two differentcategories of stents for coronary application, for example, smallvessels stents for use in vessels with diameters from 2.5 mm to 3.0 mm,and large vessel stents for use in vessels with diameters from 3.0 mm to5.0 mm. Thus, both small vessels and large vessels when treated with theappropriate sized stent will contain stents of similar idealized metalfraction.

The stent of the present invention can be made using a CAM-driven lasercutting system to cut the stent pattern from a stainless steel tube. Therough-cut stent is preferably electro-polished to remove surfaceimperfections and sharp edges. Other methods of fabricating the stentcan also be used such as EDM, photo-electric etching technology, orother methods. Any suitable material can be used for the stent includingother metals and polymers so long as they provide the essentialstructural strength, flexibility, biocompatibility and expandability.

The stent is typically at least partially plated with a radiopaquemetal, such as gold, platinum, tantalum or other suitable metal. It ispreferred to plate only both ends of the stent by localized plating;however, the entire stent or other regions can also be plated. Whenplating both ends, one to three or more expansion columns on each end ofthe stent are plated to mark the ends of the stent so they can beidentified under fluoroscopy during the-stenting procedure. By platingthe stent only at the ends, interference of the radiopaque platingmaterial with performance characteristics or surface modulation of thestent frame is minimized. Additionally the amount of plating materialrequired is reduced, lowering the material cost of the stent.

After plating, the stent is cleaned, typically with detergent, salineand ultrasonic means that are well-known in the art. The stents are theninspected for quality control, assembled with the delivery ballooncatheter, and properly packaged, labeled, and sterilized.

Stent 10 can be marketed as stand alone or as a pre-mounted deliveryballoon catheter assembly as shown in FIG. 11. Referring to FIG. 11, thestent 10 is crimped over a folded balloon 146 at the distal end 148 of adelivery balloon catheter assembly 150. The assembly 150 includes aproximal end adapter 152, a catheter shaft 154, a balloon channel 156, aguidewire channel 158, a balloon 146, and a guidewire 160. Balloon 146can be tapered, curved, or both tapered and curved from a proximal endto a distal end in the expanded state. Additionally stent 10 can benon-tapered or tapered in the expanded state.

Typically the guidewire 160 is inserted into the vein or artery andadvanced to the target site. The catheter shaft 154 is then forwardedover the guidewire 160 to position the stent 10 and balloon 146 intoposition at the target site. Once in position the balloon 146 isinflated through the balloon channel 156 to expand the stent 10 from acrimped to an expanded state. In the expanded state, the stent 10provides the desired scaffolding support to the vessel. Once the stent10 has been expanded, the balloon 146 is deflated and the cathetershaft, 154, balloon 146, and guidewire 160 are withdrawn from thepatient.

The stent of the present invention can be made as short as less than 10mm in length or as long as 100 mm or more. If long stents are to beused, however, matching length or preferably slightly longer deliverycatheter balloons will typically be needed to expand the stents intotheir deployed positions. Long stents, depending on the target vessel,may require curved long balloons, tapered long balloons or curved andtapered long balloons for deployment. Curved and/or tapered balloonswhich match the natural curve and taper of a blood vessel reduce stresson the blood vessel during and after stent deployment. This isespecially important in many coronary applications which involvestenting in curved and tapered coronary vessels. The use of such curvedand/or tapered balloons is within the scope of the present invention.

The foregoing description of a preferred embodiment of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formsdisclosed. Obviously, many modifications and variations will be apparentto practitioners skilled in this art. It is intended that the scope ofthe invention be defined by the following claims and their equivalents.

1. A stent comprising: a plurality of adjacent cylindrical elements,each cylindrical element extending around a longitudinal stent axis,wherein each cylindrical element is formed from struts arranged in aserpentine wave pattern, each of the struts having a length; wherein theplurality of adjacent cylindrical elements are arranged in alignmentalong the longitudinal stent axis, and wherein a plurality ofcylindrical elements include sequentially increasing inner diameters tocreate a tapered profile; a plurality of interconnecting membersextending between the adjacent cylindrical elements and connecting theadjacent cylindrical elements to one another, the interconnectingmembers and cylindrical elements defining a plurality of asymmetriccells which have no geometrical symmetry; and wherein the plurality ofstruts of a cylindrical element at the tapered profile has an increasedlength along the longitudinal stent axis relative to the struts in anadjacent cylindrical element.
 2. The stent of claim 1, wherein theserpentine wave pattern of a cylindrical element is out of phase withthe serpentine wave pattern of an adjacent cylindrical element.
 3. Astent comprising a plurality of expansion columns, the plurality ofexpansion columns having an outer surface and defining a flowpaththerethrough, each expansion column comprising a plurality ofinterconnected expansion struts, adjacent expansion columns connectedvia connection struts, at least a portion of both the outer surface andthe flowpath having a tapered profile extending from a first end of thestent toward the middle of the stent, the middle of the stent having alarger diameter than the first end of the stent, wherein the thicknessof the struts increases from the middle of the stent to the first end ofthe stent.
 4. A stent having an outer surface facing in a radiallyoutward direction, an inner surface facing in a radially inwarddirection, the stent comprising a plurality of expansion columns, eachexpansion column comprising a plurality of interconnected expansionstruts, adjacent expansion columns connected via connection struts, atleast a portion of the stent having a tapered profile extending from afirst end of the stent toward the middle of the stent, the middle of thestent having a larger diameter than the first end of the stent, whereinthe stent has a thickness as measured in a radial direction,. and thewidths of the struts, as measured along the outer surface of the stent,increase from the middle of the stent to the first end of the stent. 5.A stent comprising a plurality of expansion columns, each expansioncolumn comprising a plurality of interconnected expansion struts,adjacent expansion columns connected via connection struts, at least aportion of the stent having a tapered region in which the diameter ofthe stent decreases, wherein the lengths of the connection strutsprogressively decrease from a first end of the tapered region to asecond end of the tapered region, a portion of the tapered region havinga larger diameter and a portion of the tapered region having a smallerdiameter, the portion having the larger diameter having longer connectorstruts and the portion having the smaller diameter having shorterconnector struts.
 6. The stent of claim 5 further comprising connectionstruts which include at least one section which is non-parallel to thelongitudinal axis of the stent.
 7. The stent of claim 5 furthercomprising connection struts which include at least one curved section.8. The stent of claim 5 further comprising connection struts whichinclude two curved sections.
 9. The stent of claim 5 wherein theexpansion columns and the connection struts form a plurality ofasymmetric cells.